Various types of seal assemblies have been devised of the past fifty years for sealing between a casing hanger and a wellhead. Some seal assemblies are suitable for either high temperature or high pressure application, but not both high temperature and high pressure applications. Other seal assemblies are only suitable for modest temperature and pressure applications. Other seal assemblies initially form a seal, but over time lose their sealing effectiveness.
U.S. Pat. No. 6,705,615 discloses a seal assembly for sealing between a cylindrical surface and a tapered surface. Another type of seal assembly suitable for sealing between a cylindrical surface and tapered surface is disclosed in U.S. Pat. No. 6,666,276. A split carrier seal assembly for sealing between a sub-sea wellhead housing and a casing hanger is disclosed in U.S. Pat. No. 6,969,070. U.S. Pat. Nos. 4,757,860 and 5,076,356 and discloses another form of seal assembly for sealing between a cylindrical surface and a tapered surface.
U.S. Pat. No. 7,096,956 discloses a downhole tool for activating a seal assembly. U.S. Pat. No. 6,202,745 discloses a casing hanger positioned within a wellhead.
Most downhole wellhead-hanger seal assemblies are manufactured from two or more components which make up the seal body which supports one or more seals that seal with the wellhead and the hanger. In many cases, these components are interconnected by threads, which inherently allow axial travel between components. This axial travel between seal body components allows travel and thus wear on both the seals and the sealing surfaces. High seal setting forces are also conventionally difficult to transmit through a seal body with threaded components.
Another significant problem with prior art sealing assemblies is that when fluid pressure is applied from below the set seal assembly, the interior wellhead wall expands radially outward, and the exterior hanger wall contracts radially inward, thereby creating a significant increase in the radial gap, which inherently detracts from sealing effectiveness. The disadvantages of this created gap are particularly significant when high downhole pressure is applied from below the seal assembly.
The disadvantages of the prior art are overcome by the present invention, and an improved seal assembly and method are hereinafter disclosed.